fix(deps): update rust crate cortex-m-rt to 0.7.2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
cortex-m-rt	dependencies	patch	0.7.1 -> 0.7.2

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Release Notes

rust-embedded/cortex-m

### [`v0.7.2`](https://togithub.com/rust-embedded/cortex-m/blob/HEAD/CHANGELOG.md#v072---2021-03-07) [Compare Source](https://togithub.com/rust-embedded/cortex-m/compare/v0.7.1...v0.7.2) ##### Fixed - Fixed a bug where calling `asm::delay()` with an argument of 0 or 1 would underflow, leading to a very long delay.

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